1. Field of the Invention
The present invention relates generally to an internal combustion engine having a combustion heater and, more particularly, to an internal combustion engine having a combustion heater, which is constructed to enhance a low-temperature starting property of the internal combustion engine, speed up a warm-up of the internal combustion engine, enhance a performance of a heating system in a car room, and speed up a warm-up of an exhaust emission control system by raising temperatures of engine related elements such as cooling water and intake air or an exhaust gas.
2. Description of the Prior Art
It is desired that an internal combustion engine be constructed to enhance a starting property and speed up a warm-up thereof especially at a cold time. In particular, a diesel engine and other lean-burn engines are required to further enhance the starting property and a performance of the warm-up, because these engines have a less exothermic amount as compared to a general gasoline engine.
Such being the case, there has hitherto been known a technology (see, e.g., Japanese Patent Application Laid-Open Publication No.60-78819) of heating a thermal medium such as engine cooling water and the like by utilizing combustion heat emitted from a combustion heater attached to, e.g., an intake passageway of the internal combustion engine, sending the thus heated thermal medium to a water jacket of the engine body, a heater core for warming a car room and other necessary places, and raising temperatures of those necessary places.
What is suitable as a combustion heater may be a vaporization type combustion heater which vaporizes a combustion fuel of the combustion heater into a vaporized fuel, forms a latent flame by igniting this vaporized fuel, and growing the latent flame into flames.
As known well, the vaporization type combustion heater includes at least a combustion chamber for producing the flames, a fuel supply unit for supplying this combustion chamber with a liquefied fuel for the combustion, a fuel vaporizing unit for vaporizing the liquefied fuel supplied by the fuel supply unit, a glow plug serving as an igniting device for forming the latent flame by igniting the vaporized fuel vaporized by the fuel vaporizing unit, an air blow fan for growing the latent flame made by the glow plug into flames with a proper magnitude and force by controlling an air supply quantity to the latent flame, a cooling water passageway through which to flow engine cooling water which absorbs the combustion heat evolved by the flames and raises its temperature, and an air flow passageway including an air supply passageway for supplying the combustion chamber with the air for combustion and a combustion gas discharge passageway for discharging the combustion gas produced by the combustion out of the combustion chamber.
The internal combustion engine having the combustion heater disclosed in the above-mentioned Japanese Patent Application Laid-Open Publication No. 60-78819 is so configured that a portion of the intake air flowing through an intake passageway of the internal combustion engine is supplied as the air for combustion to the combustion heater, and the combustion gas of the combustion heater is discharged to an exhaust passageway of the engine.
On the occasion of supplying the combustion heater with the air for combustion, an air intake port of the combustion heater is connected to the intake passageway via an intake duct which is an air supply passageway. Further, for returning the combustion gas to the exhaust passageway, the combustion gas discharge port of the combustion heater is connected to the exhaust passageway via an exhaust duct classified which is a combustion gas discharge passageway.
Further, according to the technology disclosed in the above publication, the liquefied fuel supplied to the combustion chamber of the combustion heater is vaporized into the vaporized fuel, and the air for combustion sent to the combustion heater is pressure-supplied by the air blow fan into the combustion chamber. The air for combustion supplied by pressurization is mixed with the vaporized fuel into an air-fuel mixture, and the combustion gas produced when the air-fuel mixture is burned in the combustion chamber, is as described above discharged to the exhaust passageway via the exhaust duct.
A connecting point on the exhaust passageway where the exhaust passageway is connected to the exhaust duct is disposed upstream of a catalyst converter which is an exhaust gas purification device and disposed on the exhaust passageway. Therefore, the combustion gas flowing to the exhaust passageway via the exhaust duct is purified together with the exhaust gas discharged from the internal combustion engine by the catalyst converter.
In the case where the intake duct is connected to the intake passageway and the exhaust duct is connected to the exhaust passageway, as described above, a pressure in the exhaust passageway becomes higher than a pressure in the intake passageway due to an exhaust gas pressure depending on an operating state of the engine. Accordingly, it might be considered in this case that the combustion gas of the combustion heater is unable to flow to the exhaust passageway.
Even in such a case, however, if a supercharger is provided in the internal combustion engine having the combustion heater and a pressure of the intake air is raised by increasing a supercharging pressure of the supercharger, the intake air with the increased pressure can be introduced into the combustion heater.
If the supercharging pressure is high, however, a pressure of the air for combustion led into the combustion heater also rises. Thereupon, there increases a differential pressure between the air intake port and the combustion gas discharge port of the combustion heater, with the result that a quantity of the air flowing inside the combustion heater excessively augments, and there might be a possibility that the air blow quantity by the air blow fan of the combustion heater does not work. If the excessive air flows, this might induce a decline of the ignition in the combustion heater, or destabilized flames because of the air/fuel ratio becoming lean, or an unstable combustion, or a lean accidental fire.
On the other hand, aiming at warming up the engine and so forth, the combustion gas discharge passageway is connected to the intake passageway in place of the exhaust passageway as the case may be. That is to say, the intake duct and the exhaust duct are connected to the intake passageway.
In some cases, however, there are differences in terms of a sectional size and configuration of the intake passage between a connecting point of the intake duct to the intake passageway and a connecting point of the exhaust duct to the intake passageway. In such a case, a differential pressure is liable to occur between the connecting point of the intake duct and the connecting point of the exhaust duct.
Further, if both of the connecting points of the intake duct and of the exhaust duct are provided downstream of a supercharger, the differential pressure is further liable to occur. Hence, there might arise the problems such as the decline of the ignition and the like.
Moreover, what is exemplified as causing the problems such as the decline of ignition due to the differential pressure occurred may be a case where neither the intake duct nor the exhaust duct communicates with the intake passageway or the exhaust passageway, but both of these ducts are open to the atmospheric air, and a case where the vehicle travels at a high speed.
In the case of such settings, the differential pressure still occurs in terms of a positional relationship of the intake duct and the exhaust duct when they are mounted in the vehicle.
Further, what can be considered as causing the differential pressure may be a case where an engine rotational speed is high when the intake duct is open to the atmospheric air and the exhaust duct is connected to the intake passageway.